Background: Preliminary evidence suggests that meditation and exercise may work through interacting psychological and physiological pathways to stimulate the immune system and reduce infectious disease. Methods: In this study, women and men aged 50 and older will be randomized to: 1) an 8 week behavioral training program in mindfulness meditation, 2) an intensity, duration and location-matched 8 week exercise training program, or 3) a health education session attention control group. Sample size will be N=333, with N=111 in each group. The primary outcome will be severity-adjusted total days of acute respiratory infection (ARI) illness during 8 months of observation, as self-reported on the Wisconsin Upper Respiratory Symptom Survey, a validated questionnaire outcome measure. Nucleic acid based viral identification will verify infection. Nasal wash during ARI illness will be analyzed for inflammatory markers IL-8 and nasal neutrophil count. Secondary outcome immune biomarkers will include antibody response to influenza immunization (serum IgG, mucosal IgA) and cytokines IFN-? and IL-10 from cultured ex vivo lymphocytes. Questionnaire measures assessing perceived stress, positive and negative affectivity, optimism and anxiety will be analyzed as potential mediators of immunomodulation. Timeframe / logistics: This will be a 4 year project, with 3 annual cohorts (1st year N=75;2nd and 3rd years N=129 each). Yearly cohorts will be screened from January to August, undergo a short adherence-assessing run-in trial in September, then consent and be randomized to meditation, exercise or control starting in October. Tri-valent influenza vaccination will occur in November on week 6 of behavioral sessions. Blood for antibody titer and ex vivo cytokine assay will be drawn at baseline, at the end of the 8 week session, and once again 3 months later. Nasal swab for IgA will be done at the same time. Participants will be followed with telephone contact every two weeks, with monthly questionnaire instruments, and with daily self-assessments during ARI illness episodes. Analysis: ANOVA-based models assess effects of meditation and exercise on immune markers and ARI illness. Psychological measures will be assessed as potential mediators of effects of meditation and exercise on ARI illness. Generalized estimating equations, random-effects pattern-mixture models, and hierarchical linear models will be used to assess longitudinal effects, interactions, and covariate mediation. PUBLIC HEALTH REVELANCE: The overarching goal of this project is to determine whether mind-body practices such as meditation or exercise can reduce the public health burden of acute respiratory infection. A major secondary goal is to determine whether mindfulness meditation or moderately strenuous exercise can enhance immune processes such as antibody response to influenza vaccination (flu shots). Finally, we want to investigate the influence of stress, optimism, anxiety and positive and negative emotion on immunity and resistance to respiratory infection.